1. Field of the Invention
The present invention relates to a device for sampling gases from a furnace.
2. Description of the Prior Art
With the recent trend toward the increase in capacity of blast and vertical furnaces and the use of higher pressure, techniques must be established for operating a blast or vertical furnace at its highest efficiency in a reliable and dependable manner so that savings in expensive imported raw materials may be attained. For this purpose there has long been the demand for a device for sampling gases from a blast or vertical furnace which device is essential for the furnace operation and is highly reliable in operation and inexpensive to fabricate and install.
IN FIGS. 1 and 2, there is shown one example of the prior art furnace gas sampling devices. A lance c is inserted into a furnace body a charged with raw materials b, and is extended through a gate valve d and a sealing device e to be connected to the piston rods of lance driving cylinders f mounted on guide frames g with brackets h.
In operation, the lance 4 whose inner end is terminated into a sampling hole or port is traversed across the furnace body a over a distance substantially equal to the radius of the furnace for sampling furnace gases at several predetermined sampling points. After sampling, the inner end of the lance c is retracted over a stroke A and normally held in a lance insertion hole in the furnace wall as shown by the broken lines in FIG. 2. With the lance c in the retracted position, the gate valve d is completely closed, and the sealing device e prevents the leakage of furnace gases.
In case of failure or inspection of the lance c, the latter is further retracted from the normal position over a stroke B. In this case, when the inner end of the lance c is located between the gate valve d and the sealing device e, the gate valve d is closed to prevent the leakage of the furnace gases.
The lance c is driven by the cylinders f with a relatively long stroke in excess of the whole stroke (A + B) of the lance c. When the capacity of a furnace is of the order of more than 4,000 m.sup.3, there must be provided hydraulic cylinders with a stroke in excess of 10 meters so that many problems arise as will be described below. Firstly, there is a buckling problem of a cylinder rod with the increase in stroke so that the cylinder rod must be increased in diameter. Then a long cylinder with a large diameter is required, but it is very difficult to fabricate such a cylinder and special materials must be selected with the resultant increase in cost. In addition, the longer the piston rod, the greater the deflection becomes.
Furthermore oil leakage tends to occur from piston rod packings because of the rupture of oil films on the piston rod surface and the adhesion of dust to the surface of the piston rod. With the increase in length of the piston rod and the cylinder, the guide frames g and a deck structure for supporting the guide frames g must be increased in size accordingly so that the furnace gas sampling device becomes large in size and heavy in weight and consequently the installation cost and space are increased.
The lance c and the guide frames g must satisfactorily follow the thermal expansion of the furnace body a. However since the lance c, the guide frames g and the driving cylinders f are considerably long, it is extremely difficult to fabricate and install the furnace gas sampling device with a higher degree of accuracy so that there is a danger that excess loads are exerted to the driving cylinders f due to the thermal expansion of the furnace body a.
In the prior art furnace gas sampling devices, the gate valve d is, in general, of the slide type so that a sliding plate valve tends to bite a packing too much, causing the sealing failure; that is, the leakage of high pressure furnace gases into the surrounding atmosphere.
In general, the sealing device e is of the formed gland packing seal type. In this type, the whole gland packings must be replaced in case of repair so that skilled labors are required and the replacement is very tedious. Furthermore the clearance between the lance c and the lance sealing members of the sealing device e is very severe. If the clearance should be increased due to the abrasion, wear and thermal deformations, the leakage of furnace gases cannot be prevented.
The pin-hinged or cymbul type couplings i have long been used because they may absorb the angular displacements due to the axial thrusts or axial tensile, compressive and repeated forces, but excessive axial thrusts are exerted to the coupling, resulting in the frequent breakdowns of the coupling. Furthermore the coupling is subjected to the angular displacements in all directions due to the high temperatures so that the breakdowns of the coupling tend to occur very often. The coupling i must be installed with a higher degree of accuracy in all directions except a predetermined angle through which the angular displacement of the coupling is permitted so that the safety of the coupling against an unexpected factor such as the displacement in an unexpected direction due to the thermal expansion of the furnace body a cannot be ensured.